Increasingly stringent legislation governing the permissible noxious emissions from motor vehicles containing internal combustion engines necessitates minimizing the noxious emissions produced while the internal combustion engine is operating. That can be done on the one hand by reducing the noxious emissions occurring during combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine.
On the other hand, exhaust gas aftertreatment systems that convert the noxious emissions produced during combustion of the air/fuel mixture in the respective cylinders into harmless substances are employed in internal combustion engines.
Catalytic converters are used for that purpose which convert carbon monoxide, hydrocarbons, and nitrogen oxides into harmless substances.
Both the selective influencing of the production of noxious emissions during combustion and the conversion of noxious components with a high degree of efficiency by means of a catalytic converter require a very precisely adjusted air/fuel ratio in the respective cylinder.
Known from the technical publication titled “Handbuch Verbrennungsmotor” (appearing in English as “Internal Combustion Engine Handbook”), edited by Richard van Basshuysen and Fred Schäfer, 2nd edition, published by Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pages 559-561, is a linear lambda control system having a linear lambda probe located upstream of a catalytic exhaust gas converter and having a binary lambda probe located downstream of the catalytic exhaust gas converter. A setpoint lambda value is filtered by means of a filter that takes account of gas travel times and the sensor characteristics. The thus filtered setpoint lambda value is the control variable of a PII2D lambda controller whose correcting variable is a correction in the injected amount.
Known also from the technical publication titled “Handbuch Verbrennungsmotor” (appearing in English as “Internal Combustion Engine Handbook”), edited by Richard von Basshuysen and Fred Schäfer, 2nd edition, published by Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pages 559-561, is a binary lambda control system having a binary lambda probe located upstream of the catalytic exhaust gas converter. The binary lambda control system includes a PI controller, with the P and I components being stored in engine characteristic maps of engine speed and load. In the case of the binary lambda control system, energizing of the catalytic converter, referred to also as lambda fluctuation, is an implicit product of second-point controlling. The amplitude of the lambda fluctuation is set to approximately three percent.
In connection with lambda controlling, special significance attaches to the lambda probe(s). It is in that regard necessary, for reasons including complying with legal requirements, to suitably monitor the lambda probe.